Monthly (takes five minutes)
Check your inverter monitoring app or display once a month during peak generation months (April through September). Note the daily peak output on clear days and compare with the same period last month. A gradual downward trend without weather explanation is worth monitoring; a sudden drop warrants investigation.
Glance at the panels from the ground. If you can see obvious accumulations of bird droppings, moss, or debris from street level, they are severe enough to be causing measurable output loss.
Annually (spring)
Schedule a professional clean in late spring — March, April, or early May — before the high-output summer months begin. Use a cleaner who uses deionised water and a soft-bristle brush; avoid anyone who proposes pressure washing (which can delaminate panel edges) or abrasive materials.
While the cleaner is on the roof, ask them to report any visible physical damage, corrosion on panel frames, lifted seals at roof penetrations, or disturbed fixings. A professional who is up on the roof is your cheapest source of information about the installation's condition.
Check that bird proofing mesh (if fitted) is intact and that no sections have been pushed in or torn. Pigeons will exploit any gap.
Every two to three years
Have an electrical inspection of the DC isolators, AC isolators, and inverter connections carried out by a qualified solar technician (Part P or similar). DC cabling connections and isolator contacts can develop resistance over time, particularly in installations exposed to thermal cycling. High resistance at a connection creates a hotspot that can eventually cause a fire.
This is separate from an EICR (Electrical Installation Condition Report) for the domestic consumer unit, though the two can sometimes be combined by an MCS-qualified electrician.
Review your monitoring data for the past year and compare cumulative annual generation against your installer's original estimate. Deviation of more than 10% below estimate (after adjusting for actual sun hours versus average) suggests a system issue worth investigating.
One-offs and event-triggered checks
After any severe weather event — storm, hail, snow load — do a ground-level visual inspection the following morning. Look for cracked panels, displaced fixings, or roof tiles displaced adjacent to the array.
If you re-roof the property, the panels will need to be removed and reinstalled by a qualified solar installer. Use this as an opportunity to have the cabling and connections inspected and the inverter serviced.
If you extend, add a dormer, plant large trees, or make any change to the property that could introduce new shading on the array, review your monitoring data for the following three months to quantify any output change.
If your inverter is approaching or past the end of its manufacturer warranty period — typically 5–12 years — get a replacement quote before it fails. An unexpected inverter failure in peak summer is both an unplanned cost and lost generation; budgeting for replacement proactively is better.